What is claimed is:1. A method performed by a user equipment (UE) in a wireless communication system, the method comprising:receiving, from a base station, packet data convergence protocol (PDCP) configuration information including information indicating that a PDCP layer is configured with out-of-order delivery;identifying that the PDCP layer is configured with the out-of-order delivery based on the PDCP configuration information; andprocessing a PDCP protocol data unit (PDU) based on a result of identifying that the PDCP layer is configured with the out-of-order delivery,wherein a header compression or a header decompression are not used in case that the PDCP layer is configured with the out-of-order delivery.2. The method of claim 1, further comprising delivering a PDCP service data unit (SDU) generated based on the PDCP PDU to an upper layer, regardless of an order of a count value of the delivered PDCP SDU, in case that the PDCP layer is configured with the out-of-order delivery.3. The method of claim 2, wherein delivering the PDCP SDU further comprises omitting the header decompression before the PDCP SDU is delivered to the upper layer.4. The method of claim 1, further comprising:determining whether a count value of a received PDCP PDU is identical with a value of a state variable indicating a count value of a first PDCP service data unit (SDU) not delivered to an upper layer, in case that the PDCP layer is not configured with the out-of-order delivery;performing the header decompression on a PDCP SDU with consecutively associated count values starting from the value of the state variable indicating the count value of the first PDCP SDU not delivered to the upper layer;delivering the PDCP SDU to the upper layer in ascending order of the associated count values of the PDCP SDU, in case that the count value of the received PDCP PDU is identical with the value of the state variable indicating the count value of the first PDCP SDU not delivered to the upper layer; andupdating the value of the state variable to the count value of the first PDCP SDU which has not been delivered to upper layers, wherein the count value is greater than a previous value of the state variable, in case that the count value of the received PDCP PDU is identical with the value of the state variable indicating the count value of the first PDCP SDU not delivered to the upper layer.5. The method of claim 1, further comprising:delivering a PDCP service data unit (SDU) generated based on the PDCP PDU to an upper layer, regardless of an order of a count value of the delivered PDCP SDU, in case that the PDCP layer is configured with the out-of-order delivery;determining whether a count value of a received PDCP PDU is identical with a value of a state variable indicating a count value of a first PDCP SDU not delivered to the upper layer; andupdating the value of the state variable to the count value of the first PDCP SDU which has not been delivered to upper layers, wherein the count value is greater than a previous value of the state variable, in case that the count value of the received PDCP PDU is identical with the value of the state variable indicating the count value of the first PDCP SDU not delivered to the upper layer.6. A user equipment (UE) in a wireless communication system, the UE comprising:a transceiver; anda controller configured to:receive, from a base station via the transceiver, packet data convergence protocol (PDCP) configuration information including information indicating that a PDCP layer is configured with out-of-order delivery,identify that the PDCP layer is configured with the out-of-order delivery based on the PDCP configuration information, andprocess a PDCP protocol data unit (PDU) based on a result of identifying that the PDCP layer is configured with the out-of-order delivery,wherein a header compression or a header decompression are not used based on the PDCP layer being configured with out-of-order delivery.7. The UE of claim 6, wherein the controller is further configured to deliver a PDCP service data unit (SDU) generated based on the PDCP PDU to an upper layer, regardless of an order of a count value of the delivered PDCP SDU, in case that the PDCP layer is configured with the out-of-order delivery.8. The UE of claim 7, wherein the controller is further configured to omit the header decompression before the PDCP SDU is delivered to the upper layer.9. The UE of claim 6, wherein the controller is further configured to:determine whether a count value of a received PDCP PDU is identical with a value of a state variable indicating a count value of a first PDCP service data unit (SDU) not delivered to an upper layer, in case that the PDCP layer is not configured with the out-of-order delivery,perform the header decompression on a PDCP SDU with consecutively associated count values starting from the value of the state variable indicating the count value of the first PDCP SDU not delivered to the upper layer,deliver the PDCP SDU to the upper layer in ascending order of the associated count values of the PDCP SDU, in case that the count value of the received PDCP PDU is identical with the value of the state variable indicating the count value of the first PDCP SDU not delivered to the upper layer, andupdate the value of the state variable to the count value of the first PDCP SDU which has not been delivered to upper layers,wherein the count value is greater than a previous value of the state variable, in case that the count value of the received PDCP PDU is identical with the value of the state variable indicating the count value of the first PDCP SDU not delivered to the upper layer.10. The UE of claim 6, wherein the controller is further configured to:deliver a PDCP service data unit (SDU) generated based on the PDCP PDU to an upper layer, regardless of an order of a count value of the delivered PDCP SDU, in case that the PDCP layer is configured with the out-of-order delivery,determine whether a count value of a received PDCP PDU is identical with a value of a state variable indicating a count value of a first PDCP SDU not delivered to the upper layer, andupdate the value of the state variable to the count value of the first PDCP SDU which has not been delivered to upper layers, wherein the count value is greater than a previous value of the state variable, in case that the count value of the received PDCP PDU is identical with the value of the state variable indicating the count value of the first PDCP SDU not delivered to the upper layer.11. A method performed by a base station in a wireless communication system, the method comprising:generating packet data convergence protocol (PDCP) configuration information including information indicating that a PDCP layer of a user equipment (UE) is configured with out-of-order delivery; andtransmitting the PDCP configuration information to the UE,wherein a header compression or a header decompression are not used in case that the PDCP layer is configured with the out-of-order delivery.12. The control method of claim 11, wherein a PDCP service data unit (SDU) generated based on a PDCP protocol data unit (PDU) is delivered to a higher layer regardless of an order of a count value of the PDCP SDU, in case that the PDCP layer of the UE is configured with the out-of-order delivery.13. The control method of claim 12, wherein the header decompression before the PDCP SDU is delivered to the upper layer is omitted.14. The method of claim 11,wherein whether a count value of a received PDCP PDU is identical with a value of a state variable indicating a count value of a first PDCP SDU not delivered to an upper layer is determined, in case that the PDCP layer is not configured with the out-of-order delivery,wherein the header decompression on a PDCP service data unit (SDU) with consecutively associated count values starting from the value of the state variable indicating the count value of the first PDCP SDU not delivered to the upper layer is performed, and the PDCP SDU is delivered to the upper layer in ascending order of the associated count values of the PDCP SDU, in case that the count value of the received PDCP PDU is identical with the value of the state variable indicating the count value of the first PDCP SDU not delivered to the upper layer, andwherein the value of the state variable to the count value of the first PDCP SDU which has not been delivered to upper layers, the count value being greater than a previous value of the state variable, is updated in case that the count value of the received PDCP PDU is identical with the value of the state variable indicating the count value of the first PDCP SDU not delivered to the upper layer.15. The method of claim 11,wherein a PDCP service data unit (SDU) generated based on the PDCP PDU is delivered to an upper layer, regardless of an order of a count value of the delivered PDCP SDU, in case that the PDCP layer is configured with the out-of-order delivery;wherein whether a count value of a received PDCP PDU is identical with a value of a state variable indicating a count value of a first PDCP SDU not delivered to the upper layer is determined, andwherein the value of the state variable to the count value of the first PDCP SDU which has not been delivered to upper layers, wherein the count value is greater than a previous value of the state variable, is updated in case that the count value of the received PDCP PDU is identical with the value of the state variable indicating the count value of the first PDCP SDU not delivered to the upper layer.16. A base station in a wireless communication system, the base station comprising:a transceiver; anda controller configured to:generate packet data convergence protocol (PDCP) configuration information including information indicating that a PDCP layer of a user equipment (UE) is configured with out-of-order delivery, andtransmit the PDCP configuration information to the UE via the transceiver,wherein a header compression or a header decompression are not used in case that the PDCP layer being configured with the out-of-order delivery.17. The base station of claim 16, wherein a PDCP service data unit (SDU) generated based on a PDCP protocol data unit (PDU) is delivered to a higher layer, regardless of an order of a count value of the PDCP SDU, in case that the PDCP layer of the UE is configured with the out-of-order delivery.18. The base station of claim 17,wherein the header decompression before the PDCP SDU is delivered to the upper layer is omitted.19. The base station of claim 16,wherein whether a count value of a received PDCP PDU is identical with a value of a state variable indicating a count value of a first PDCP SDU not delivered to an upper layer is determined, in case that the PDCP layer is not configured with the out-of-order delivery,wherein the header decompression on a PDCP service data unit (SDU) with consecutively associated count values starting from the value of the state variable indicating the count value of the first PDCP SDU not delivered to the upper layer is performed, and the PDCP SDU is delivered to the upper layer in ascending order of the associated count values of the PDCP SDU, in case that the count value of the received PDCP PDU is identical with the value of the state variable indicating the count value of the first PDCP SDU not delivered to the upper layer, andwherein the value of the state variable to the count value of the first PDCP SDU which has not been delivered to upper layers, the count value being greater than a previous value of the state variable, is updated in case that the count value of the received PDCP PDU is identical with the value of the state variable indicating the count value of the first PDCP SDU not delivered to the upper layer.20. The base station of claim 16,wherein a PDCP service data unit (SDU) generated based on the PDCP PDU is delivered to an upper layer, regardless of an order of a count value of the delivered PDCP SDU, in case that the PDCP layer is configured with the out-of-order delivery,wherein whether a count value of a received PDCP PDU is identical with a value of a state variable indicating a count value of a first PDCP SDU not delivered to the upper layer is determined, andwherein the value of the state variable to the count value of the first PDCP SDU which has not been delivered to upper layers, wherein the count value is greater than a previous value of the state variable, is updated in case that the count value of the received PDCP PDU is identical with the value of the state variable indicating the count value of the first PDCP SDU not delivered to the upper layer.